In the oil and gas industry, acoustic tools are used to provide operationally significant information about seismic events occurring during production of a well. Borehole seismic data can be utilized to determine subsurface stratigraphy and refine surface seismic data. Micro-seismic data may be generated by formation fracturing—induced or natural. The acoustic tools may include seismic sensors such as geophones, geophone accelerometers, hydrophones, or other types of sensors known in the art.
In the past, downhole seismic data has been acquired by a number of different techniques. An array of seismic devices having seismic sensors may be deployed into a borehole, and when the seismic devices reach a desired depth, they may be mechanically coupled to a borehole wall, casing and/or be cemented in place. In other instances, seismic tools with sensors may be coupled to production tubing, inside a well, or in association with production packers.
A conventional method for deploying a seismic device in a borehole may utilize a winch mechanism. The winch mechanism may include a winch drum and a cable, which may be a wireline and is wound around the drum. A plurality of seismic devices are attached to the cable spaced apart from each other. The drum is rotatably supported on the winch and, as the drum rotates counterclockwise, the cable unwinds from the drum and descends into the borehole with the sensors.
Conventional methods have encountered many problems. For example, the seismic devices may be attached to the cable by means of an electrical mechanism and a mechanical mechanism, and thus form large and less flexible nodes on the cable. When such a seismic array is wound onto a winch drum, the nodes may form numerous bulges. Thus, the seismic array may not be uniformly wound onto the winch drum, which may lead to inefficient use of space and potential entanglement of the cable and nodes. Although a triangle drum has been considered by people having ordinary skill in the art for deploying a seismic device array with large-sized sensors, such as a VSI (Versatile Seismic Imager), this kind of drum has a limitation on the number of layers of the array around the drum and hence the length of the array. Further, in conventional methods, a large-sized drum may be needed for an array having a large number of seismic devices and will take up a large space near a rig, which is not desirable.
There are also other conventional methods for deploying an array having a plurality of seismic devices into a borehole without using a winch drum, such as deploying seismic devices one by one into the borehole. Such methods, however, are time-consuming and it may take, for example, 5 to 10 minutes per node or shuttle, to deploy such an array into a borehole.